Abstract: Yaw-checking and course-keeping ability in IMO's ship manoeuvrability standards is reviewed from the viewpoint of safe navigation. Three kinds of virtual series-ships, which have different course instability, are taken as test models. The numerical simulation on Z-test is carried out in order to examine the correlation between known manoeuvrability in spiral characteristics and various kinds of overshoot angle. Then simulator experiments are executed with series-ships in a curved, narrow waterway by six operators (five active pilots and one ex-captain) in order to examine the correlation between known manoeuvrability and degree of manoeuvring difficulty. IMO criteria for yaw-checking and course-keeping ability are discussed and revised criteria are proposed.

　

 Recent marine disaster of large ships often causes serious oil pollution. To prevent or reduce such a disaster, International Maritime Organization (IMO) has been endeavoring to improve ship's manoeuvrability, and adopted the interim standards for ship manoeuvrability A751(18) in 1993[1]. These standards cover the typical manoeuvrability including turning ability, initial turning ability, yaw-checking and course-keeping ability, and stopping ability.

　

 In this paper, the authors review the manoeuvrability standards particularly focusing the criteria for the yaw-checking and course-keeping ability. Firstly, the authors take three kinds of ship built in Korea recently, from which they prepare the virtual series-ships with systematically different spiral loop widths, and carry out numerical simulation on Z-test to examine the yaw-checking and course-keeping ability of the series-ships in terms of overshoot angles. Then, simulator experiment is carried out to grasp the correlation between known manoeuvrability and degree of manoeuvring difficulty felt by pilots. Finally, the IMO's standards are discussed, and revised criteria are proposed and compared each to each in view of degree of manoeuvring difficulty.

　

2.1 Series-ships for calculation of overshoot angels

　

 The authors take a training ship, a container ship and a bulk carrier as test models for the present study. Table 1 shows principal dimensions of three actual-ships. The authors prepare three models of series-ships with different, systematic manoeuvrability. In this paper, four linear hull derivatives will change gradually their value for consideration of stern frame line, such as U or V shape 01 stern body. In order to realize this, the authors refer to the experimental result on the effect of stern frame shape on linear derivatives, which was carried out in SR221 project[2]. And simultaneously rudder area ratios will also change gradually their value for consideration of profile effect at stern. The other coefficients and non-linear hull derivatives will not change their value. The mathematical model for simulation will be mentioned in following section. Fig.1 shows simulated spiral curves of three models of series-ships with various spiral loop widths from 0) to 10 degrees at intervals of 2.5 degrees.